During X-ray imaging, it is required that an X-ray detector is always centered with respect to an X-ray beam from an X-ray source. For this reason, a conventional X-ray imaging apparatus may be provided including an X-ray source and an X-ray detector mechanically coupled to each other. Due to the mechanical coupling between the X-ray source and the X-ray detector, the X-ray detector may automatically follow the motion of the X-ray source and thus is always centered with respect to an X-ray beam from the X-ray source. However, as the mechanical coupling may limit relative motion between the X-ray source and the X-ray detector, the X-ray detector may not follow the rotation of the X-ray source and thus the apparatus cannot be used in those cases where the X-ray source is rotated; meanwhile, in such an apparatus, the height of a table on which a subject is disposed cannot be varied since the X-ray detector is usually attached to the table and thus the table's motion may be limited by the mechanical coupling also.
Another kind of X-ray imaging apparatus provides a non-mechanical coupling between an X-ray source and an X-ray detector. In this case, a laser is used for sensing the position and translation of the X-ray source, and a microcontroller is used for generating a control signal in accordance with the sensed position and translation to translate the X-ray detector so as to be always centered with respect to an X-ray beam from the X-ray source. However, the apparatus needs to incorporate a comparatively complex optical detecting system to sense the position and translation of the X-ray source unit and perform complex computations using the microcontroller to convert the sensed position and translation into a control signal for translating the X-ray detector.
US 2006/109958 A1 presents a method and system of aligning an x-ray detector and x-ray tube for data acquisition. The x-ray detector and x-ray tube are equipped with transmitters and receivers designed to provide feedback relating to the orientation, spacing, and general position thereof so as to assist the user to manually position the x-ray tube and x-ray detector relative to one another for data acquisition.
US 2004/105526 A1 presents a digital radiographic imaging system includes an offset table for determining mechanical and structural offsets which would, if not corrected, misalign the source and detector during use. Such offset table is used for calibration of the alignment between the source and detector.